Prestressing and damping of piezo ceramic type nozzles

ABSTRACT

A method for insuring that a good mechanical coupling exists between a tubular type nozzle and a surrounding ring made of piezoelectric ceramic material is provided.

Unlted States Patent 1191 1111 3,850,717 Keur et a1. 1 1 Nov. 26, 1974 [54] PRESTRESSING AND DAMPING ()F PIEZO 3,479,729 11/1969 Britt 129/2535 3,631,511 12/1971 Keur ct 111.. 346/75 CERAMIC TYPE NOZZLES 3,674,586 7/1972 Rimkus l 156/294 1 n o b t Keur, Nlles; Gerry 3,725,986 4/1973 Hoogenhoomu... 2905.35 Andeen, Menlo Park, both of Calif. 3,755,043 8/1973 lgarashi et a1. 156/272 [73] Assignee: A. B. Dick Company, Chicago, 111. 22 Fil d; 3 197 Primary Examiner-Charles E. Van Horn Assistant Examiner-F. Frisenda [2]] Appl' 4201769 Attorney, Agent, or Firm-Lindenberg, Freilich,

Wasserman, Rosen & Fernandez [52] US. Cl ..l 156/86, 29/25.35, 156/165, 156/272, 156/294 [51] Int. Cl. B29C 27/00 57 ABSTRACT [58] Field of Search 156/86, 160, 165, 295,

, 156/272, 48, 84, 85, 198, 275, 293, 29 A method for insuring that a good mechanical cou- 3133; 346/75; 29/2535; 310/8 pling exists between a tubular type nozzle and a surrounding ring made of piezoelectric ceramic material [56] References Cited is provided UNITED STATES PATENTS 3,465.35] 9/1969 Keur et a1. 346/75 4 Claims, 2 Drawing Figures PATENTEL HUVZB I974 SOURCE.

PRESTRESSING AND DAMPING OF PIEZO CERAMIC TYPE NOZZLES FIELD OF THE INVENTION This invention relates to apparatus for printing using ink drops, and more particularly to an improvement in the technique of manufacturing such apparatus. I

An ink drop printing apparatus of a type such as is described in US. Pat. No. 3,631,511, employs a cylindrical nozzle, usually made of metal, to which a piezoelectric ceramic tube is bonded. Ink under pressure is applied to the nozzle while a signal at a suitable frequency is applied to the piezoelectric ceramic tube. The piezoelectric tube expands and contracts radially in response to the signal, in the course of which it causes constrictions on the nozzle which cause the ink stream emitted from the nozzle to break down into ink drops at a corresponding frequency.

This invention also relates to an ink apparatus for printing which provides an independent fluid drop for each electric pulse applied to it. With these types of nozzles, ink is delivered to the orifice at approximately zero hydrostatic head, but it also may be delivered at slightly positive or slightly negative hydrostatic head. An electric pulse is applied to a piezoelectric cylinder surrounding a nozzle. This pulse causes the cylinder to contract and squeeze or eject a drop of fluid from the orifice. Once the drop is ejected the nozzle returns to its original state and during this time the fluid is replenished at the orifice by means of its surface tension acting at the orifice.

Difficulties have been encountered in bonding or properly mechanicallly coupling the piezoelectric ceramic material to the nozzle, and also in eliminating unwanted mechanical resonances. Poor mechanical coupling prevents efficient nozzle excitation. Unwanted resonances cause improper and/or unwanted drop formation.

OBJECT AND BRIEF DESCRIPTION OF THE INVENTION An object of this invention is to provide a method and means for bonding a piezoelectric ceramic tube to a tubular type nozzle to provide a void free bond.

Another object of this invention is the provision of an arrangement for eliminating unwanted mechanical resonances from the ceramic tube and nozzle assembly.

These and other objects ofthe invention are achieved by applying a suitable bonding agent between the ceramic tube and the tubular nozzle. During the hardening time of the bonding agent a potential is applied to the ceramic tube to maintain it in its expanded state. After the bond is hardened, the potential is removed. Once the mechanical bond has been ascertained as acceptable, the assembly is potted in an acoustic absorbing material such as RTV silastic or soft epoxy. This damps out unwanted mechanical resonances.

FIG. I illustrates the appearance of an embodiment of this invention, and FIG. 2 is a cross-sectional representation of the embodiment of the invention shown in FIG. I.

DESCRIPTION OF THE PREFERRED EMBODIMENT Radially expanding ceramics in the form ol a cylinder ameter, the inside diameter of theceramic will expand mechanically.

Referring now to FIGS. 1 and 2, respectively illustrating the embodiment of the invention and an enlarged cross-sectional view thereof, a nozzle 10, usually made of metal, has mounted thereon a piezoelectric ceramic cylinder 12. The manner of mounting, as represented in FIG. 10, is to apply a suitable bonding agent I4, at the interface between the caramiic and the tube. The bonding agent is allowed to harden, thus insuring that the tube will stay in position on the nozzle when it is electrically excited.

However, it has been found that voids occur in the bonding interface between the ceramic and the tube upon hardening of the bonding agent. As a result, there is an imperfect transmittal of compressive forces between the piezoelectric ceramic material and the ink jet mozzle. This leads to inefficient use of power and poor drop formation.

In accordance with this invention, as soon as the bonding agent has been applied to the surface of the nozzle and the ceramic tube is fitted in place, a potential source, 16, is connected between the ceramic material and the surface of the nozzle whereby it is applied to the interior of the ceramic material. This causes the ceramic material to expand radially. This potential is maintained over the entire interval required for the bonding agent to harden. After the bond has hardened, the potential is removed and the ceramic material is allowed to shrink onto the nozzle, thereby keeping the bond and the nozzle in compression and the ceramic material in tension. By this technique, voids in the bonding agent are minimized or eliminated and shrinkage of the bonding agent during hardening is of little consequence. It is preferable to have bonding agents that are energy absorbing.

After the above process is complete, the presence of a good mechanical bond can be detected by testing with any suitable electric impedance meter. Mechanical resonances can easily be seen as low impedance areas as the frequency applied to the piezoelectric material is varied.

Once it has been ascertained that the mechanical bond is good, it is now necessary to minimize or damp these mechanical resonances. This is accomplished by potting the nozzle assembly in an acoustic absorbing material such as RTV silastic or soft epoxy. This is represented by the cylinder 18 which surrounds the previously fabricated ceramic tube and nozzle assembly. The acoustic absorbing material darnps the mechanical resonances and renders a highly efficient nozzle assembly with a flat mechanical response.

There has accordingly been described and shown herein a novel and useful method and means for providing an excellent mechanical coupling between the piezoelectric cylinder and the nozzle and for eliminating undesired mechanical resonances.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I. The method of bonding a piezoelectric cylinder to a cylindrical nozzle comprising applying a bonding agent to cover a portion of the outer surface of said nozzle,

fitting said piezoelectric cylinder over said portion of the outer surface of said nozzle covered by said bonding agent,

applying a potential to said piezoelectric cylinder to cause it to expand radially,

maintaining said applied potential until said bonding agent has hardened, and

removing said potential from said piezoelectric cylinder to allow said cylinder to press down on said bonding agent and outer surface of said nozzle.

2. The method of bonding as recited in claim 1 wherein there is included the steps of potting the region of said nozzle and piezoelectric cylinder in an acoustic absorbing material.

3. The method of eliminating voids in the bonding agent employed for bonding a piezoelectric cylinder to the outer surface of a nozzle, comprising applying a bonding agent between said cylinder and eliminate mechanical resonances. 

1. The method of bonding a piezoelectric cylinder to a cylindrical nozzle comprising applying a bonding agent to cover a portion of the outer surface of said nozzle, fitting said piezoelectric cylinder over said portion of the outer surface of said nozzle covered by said bonding agent, applying a potential to said piezoelectric cylinder to cause it to expand radially, maintaining said applied potential until said bonding agent has hardened, and removing said potential from said piezoelectric cylinder to allow said cylinder to press down on said bonding agent and outer surface of said nozzle.
 2. The method of bonding as recited in claim 1 wherein there is included the steps of potting the region of said nozzle and piezoelectric cylinder in an acoustic absorbing material.
 3. The method of eliminating voids in the bonding agent employed for bonding a piezoelectric cylinder to the outer surface of a nozzle, comprising applying a bonding agent between said cylinder and said outer surface of said nozzle, applying a potential to said piezoelectric cylinder to cause it to expand radially, maintaining said applied potential until said bonding agent has hardened, and removing said potential from said cylinder to allow said cylinder to press down on said bonding agent and said outer surface of said nozzle, thereby eliminating voids in said bonding agent.
 4. The method as recited in claim 3 wherein there is included the step of potting the region of said piezoelectric cylinder and nozzle in acoustic compound to eliminate mechanical resonances. 